Objective: Identify and correct the most common stitching faults on the Janome MC6650 so your seams stay clean and sellable.
Most sewing faults are not machine defects — they are threading or tension issues, and the fabric tells you which. Loops on the BOTTOM (underside) of your fabric almost always mean the UPPER thread is wrong: it was threaded with the presser foot DOWN (so the thread never seated in the tension discs), or the upper tension is too loose. Loops or a tight ridge on the TOP mean the BOBBIN is the issue — wrong winding, or the thread not pulled into the bobbin case slot. Skipped stitches usually mean a dull, bent, or wrong-size needle, or a needle inserted backwards (the flat side of the shank must face the back). Thread breaking points to too-high tension, a nick in the needle, or thread caught on the spool. The golden rule on the MC6650: always raise the presser foot before threading so the tension discs open, and always re-seat the thread when something goes wrong rather than forcing it. To undo a bad seam, use a seam ripper: slide the point under every third or fourth stitch on one side, cut, then pull the opposite thread to lift the whole row, and brush away the cut bits.
Example: You sew a test seam on cotton and flip it over: the underside shows loose loops of thread. Reading the evidence — loops on the bottom = upper-thread fault. You lift the presser foot (opening the tension discs), unthread completely, and re-thread the top path, confirming the thread snaps crisply into the take-up lever. You sew again: loops gone, stitches now lock in the middle of the fabric layers. The problem was that the first time you threaded with the foot down, so the thread never engaged the tension discs.
Try it: Deliberately create a fault to practice diagnosis: thread the upper thread with the presser foot DOWN, then sew a 10 cm line on scrap cotton. Flip it and observe the loops underneath. Now fix it: raise the foot, re-thread fully, and sew again. Finally, take your bad seam and remove it with a seam ripper — cut every few stitches on one side, pull the other thread free, and brush off the debris. Compare the before and after.